docs: def _get_signature(self):
          """
          Returns a 32-character hexadecimal md5 hash of the signature string.
          """
  
          keys = list(self.params.keys())
  
          keys.sort()
  
          string = ""
  
          for name in keys:
              string += name
              string += self.params[name]
  
          string += self.api_secret
  
          return md5(string)